Looks like geography was ultimately to blame for the rift between Michelle Williams and Jason Segel. That's the word from People, which says the actress called time on their year-old relationship because she didn't feel they were on firm-enough footing to push forward.

"She cares a great deal for Jason but is not ready to make a commitment," explains an insider. "Maybe if they were together day-to-day, she would have more confidence in a future. But not at this time."

The main stumbling block was apparently being based on opposite coasts.

"Jason never got rid of his place in L.A., and Michelle's life with [7-year-old daughter] Matilda was and has always been in New York," chimes in another spy. "While Jason made every effort to make them a priority in his life -- and they were top priority -- he still couldn't drop everything and leave his life and career in L.A."

Not to mention his extensive puppet collection, which we assume will get an earful about his newly single status.

Meanwhile, differing levels of commitment also played a role in the recent split of Rachel McAdams and Michael Sheen. Click on …